How do I get the objects pointed to by a many-to-many association proxy to
be sorted? In the example below, adding order_by=b.order to the backref()
produces AttributeError: 'RelationshipProperty' object has no attribute
'order', and adding order_by="b.order" produces AttributeError: 'Table'
object has no attribute 'order'. Is it possible to somehow specify order_by
so that the a.bs are automatically sorted by b.order?
Thanks!
Seth
from sqlalchemy import Column, Integer, ForeignKey, create_engine
from sqlalchemy.orm import create_session, relationship, backref
from sqlalchemy.ext.declarative import declarative_base
from sqlalchemy.ext.associationproxy import association_proxy
sqlite = 'sqlite:///test_a_to_b.db'
e = create_engine(sqlite, echo=False)
Base = declarative_base(bind=e)
class A(Base):
__tablename__ = 'a'
id = Column(Integer, primary_key=True)
bs = association_proxy("a_to_b", "b", creator=lambda x: A_to_B(b=x))
class B(Base):
__tablename__ = 'b'
id = Column(Integer, primary_key=True)
order = Column(Integer)
class A_to_B(Base):
__tablename__ = 'a_to_b'
id = Column(Integer, primary_key=True)
a_id = Column(Integer, ForeignKey(str(A.__table__) + ".id"),
nullable=False, index=True)
b_id = Column(Integer, ForeignKey(str(B.__table__) + ".id"),
nullable=False)
b = relationship(B, foreign_keys=[b_id])
a = relationship(A, foreign_keys=[a_id],
backref=backref("a_to_b", lazy="subquery",
cascade="all, delete-orphan")) # , order_by="b.order"))
def __init__(self, a=None, b=None):
self.a = a
self.b = b
if __name__ == '__main__':
Base.metadata.drop_all()
Base.metadata.create_all()
session = create_session(bind=e, autocommit=False)
a = A(bs=[B(order=10), B(order=2)])
session.add(a)
session.commit()
a = session.query(A).one()
for b in a.bs:
print b.order
session.close_all()
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